The present invention relates to an image outputting apparatus for outputting a computer graphic image in which picture data of points on a texture pattern are mapped to picture data of dots on a display plane.
An image outputting apparatus outputs onto a display plane a three-dimensional (3D) computer graphic image in which luminances and colors of points in a portion of a texture pattern are projected onto luminances and colors of dots in a portion of the display plane. The appearance of the dots with the transformed picture data on the display plane is distinguishable from the appearance of other dots with non-transformed picture data thereon. This image outputting apparatus is very useful for engineers to check the result of an engineering design or to evaluate the appearance of an output image on a development phase.
Hereinafter, the mapping of the picture data of points on the texture pattern to the picture data of dots on the display plane is called the texture mapping.
In a conventional image outputting apparatus of the above type, a two-dimensional texture pattern is divided into line segments in parallel to scanning lines. Picture elements of dots on the display plane are generated by scanning the line segments in the scanning line direction. To realize this, it is necessary to carry out inverse perspective transformation for each of the picture elements of the dots.
The above conventional apparatus must perform matrix operations for each of picture elements of dots on the display plane. Thus, the processing speed is considerably low. Also, in some case of the mapping of picture data of a unit polygon from the texture pattern to picture data of a unit polygon on the display plane, the above conventional apparatus is difficult to obtain an accurate result of the texture mapping. In such a case, an output graphic image with a low quality may be produced by the above conventional apparatus.
Japanese Laid-Open Patent Application No.63-80375 discloses an image outputting apparatus in which the above problems are eliminated. The purpose of this conventional apparatus is to carry out a special-effect imaging function with a better picture quality and a higher processing speed. This special-effect imaging is carried out by making use of the texture mapping described above.
The conventional apparatus, disclosed in the above-mentioned publication, outputs an image in which picture data of points on the two-dimensional texture pattern are projected onto picture data of dots of a polygon (or a surface of an object) on the display plane. This conventional apparatus includes an I/O (input-output) interface unit, a memory, a line segment digital differential analyzer, a scan line digital differential analyzer, and others.
However, generally, picture data of all points in a texture pattern are arranged in a matrix formation, similarly to picture data of a graphic image stored in a frame memory. For example, in order to prepare a texture pattern whose picture data are arranged in a formation of a matrix of 256.times.256dots, a total of 2.sup.16 colors for picture data of the texture pattern is required. Supposing that a binary representation of one color consists of 3.times.8bits (R, G, B) of information, a storage capacity of a memory for storing the picture data of the texture pattern in this example must be about 1.5 megabits (=3.times.8bits.times.2.sup.16).
Therefore, in order to realize the special-effect imaging on an image outputting apparatus, it is necessary to incorporate a large number of memories for storing various texture patterns into the apparatus. Such texture patterns are used for outputting images of different frames on the display plane when the special-effect imaging is carried out. The apparatus into which various memories are incorporated is excessively large in size, and the cost of the manufacture is increased considerably. Accordingly, the approach of the above conventional apparatus is unsuitable for practical use.